.\"	$OpenBSD: fseek.3,v 1.16 2013/07/17 05:42:11 schwarze Exp $
.\"
.\" Copyright (c) 1990, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: July 17 2013 $
.Dt FSEEK 3
.Os
.Sh NAME
.Nm fgetpos ,
.Nm fseek ,
.Nm fseeko ,
.Nm fsetpos ,
.Nm ftell ,
.Nm ftello ,
.Nm rewind
.Nd reposition a stream
.Sh SYNOPSIS
.In stdio.h
.Ft int
.Fn fgetpos "FILE *stream" "fpos_t *pos"
.Ft int
.Fn fseek "FILE *stream" "long offset" "int whence"
.Ft int
.Fn fseeko "FILE *stream" "off_t offset" "int whence"
.Ft int
.Fn fsetpos "FILE *stream" "const fpos_t *pos"
.Ft long
.Fn ftell "FILE *stream"
.Ft off_t
.Fn ftello "FILE *stream"
.Ft void
.Fn rewind "FILE *stream"
.Sh DESCRIPTION
The
.Fn fseek
function sets the file position indicator for the stream pointed to by
.Fa stream .
The new position, measured in bytes, is obtained by adding
.Fa offset
bytes to the position specified by
.Fa whence .
If
.Fa whence
is set to
.Dv SEEK_SET ,
.Dv SEEK_CUR ,
or
.Dv SEEK_END ,
the offset is relative to the
start of the file, the current position indicator, or end-of-file,
respectively.
A successful call to the
.Fn fseek
function clears the end-of-file indicator for the stream and undoes
any effects of the
.Xr ungetc 3
function on the same stream.
.Pp
The
.Fn fseeko
function is identical to
.Fn fseek
except that it takes an
.Li off_t
as its
.Fa offset .
.Pp
The
.Fn ftell
function obtains the current value of the file position indicator for the
stream pointed to by
.Fa stream .
.Pp
The
.Fn ftello
function is identical to
.Fn ftell
except that its return value is of type
.Li off_t .
.Pp
The
.Fn rewind
function sets the file position indicator for the stream pointed
to by
.Fa stream
to the beginning of the file.
It is equivalent to:
.Pp
.Dl (void)fseek(stream, 0L, SEEK_SET)
.Pp
except that the error indicator for the stream is also cleared
(see
.Xr clearerr 3 ) .
.Pp
The
.Fn fgetpos
and
.Fn fsetpos
functions are alternate interfaces equivalent to
.Fn ftell
and
.Fn fseek
(with whence set to
.Dv SEEK_SET ) ,
setting and storing the current value of
the file offset into or from the object referenced by
.Fa pos .
On some systems an
.Dq Fa fpos_t
object may be a complex object
and these routines may be the only way to portably reposition a text stream.
.Sh RETURN VALUES
The
.Fn rewind
function returns no value.
Upon successful completion,
.Fn fgetpos ,
.Fn fseek ,
.Fn fseeko ,
and
.Fn fsetpos
return 0 and
.Fn ftell
and
.Fn ftello
return the current offset.
Otherwise,
.Fn fseek ,
.Fn fseeko ,
.Fn ftell ,
and
.Fn ftello
return \-1 and
.Fn fgetpos
and
.Fn fsetpos
return a non-zero value and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn fgetpos ,
.Fn fseek ,
.Fn fseeko ,
.Fn fsetpos ,
.Fn ftell ,
.Fn ftello ,
and
.Fn rewind
functions will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa stream
specified is not a seekable stream.
.El
.Pp
Additionally, the
.Fn fseek
and
.Fn fseeko
functions will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa whence
argument was not
.Dv SEEK_SET ,
.Dv SEEK_END ,
or
.Dv SEEK_CUR .
.El
.Pp
Additionally, the
.Fn ftell
function will fail if:
.Bl -tag -width Er
.It Bq Er EOVERFLOW
The value of the file position indicator is too large to be represented by a
.Vt long .
.El
.Pp
Finally, the functions
.Fn fgetpos ,
.Fn fseek ,
.Fn fseeko ,
.Fn fsetpos ,
.Fn ftell ,
and
.Fn ftello
may also fail and set
.Va errno
for any of the errors specified for the routines
.Xr fflush 3 ,
.Xr fstat 2 ,
.Xr lseek 2 ,
and
.Xr malloc 3 .
.Sh SEE ALSO
.Xr lseek 2
.Sh STANDARDS
The
.Fn fgetpos ,
.Fn fsetpos ,
.Fn fseek ,
.Fn ftell ,
and
.Fn rewind
functions conform to
.St -ansiC
and
.St -xpg4 .
.Pp
The
.Fn fseeko
and
.Fn ftello
functions conform to
.St -xpg4 .
.Sh HISTORY
The functions
.Fn fseek ,
.Fn ftell ,
and
.Fn rewind
first appeared in
.At v7 .
